forumbit level 2 post is the display for the forum section, using an image as the background of the table will give you the effect.
to do this on a per forum basis you would need to use the forumid variable (which should be in that template, im not sure on vb4.
but your end result should be along the lines of
Code:
<td style="background: url(path/to/image/$forum[forumid].png)">
then you would just name your images what ever the ID of the forum is.